The presently described technology relates generally to evaluation of ground-fault circuit interrupters (hereinafter “GFCI”). In particular, the present technology relates to a system and method for testing the condition or status of a GFCI.
Safety in electronic appliances and devices has become an increasing concern. Receptacles installed in homes or businesses may be capable of protecting people from injury when ground-fault conditions occur. Thus, GFCIs may be configured to interrupt electrical current upon detection of a ground-fault condition occurring at an alternating current (AC) load.
Many electrical wiring devices including receptacles have a line side that is connectable to an electrical power supply, a load side that is connectable to one or more loads, and at least one conductive path between the line side and the load side. When a person comes in contact with the line side of the AC load and an earth ground at the same time, injury may occur because the human body may form a conductive path for the electrical current to flow through.
GFCI devices may detect a ground-fault condition and break the electric power supply by employing a sensing transformer to detect an imbalance between the currents flowing in a phase (also known as “hot”) conductive path and neutral conductive path of a power supply. A ground-fault condition happens when the current is diverted to the ground through another path (e.g. a human body), that results in an imbalance between the currents flowing in the phase and neutral conductive paths. Upon detection of a ground-fault condition, a breaker or other disconnecting mechanism in a GFCI device is tripped to interrupt the electrical continuity.
A revision of the National Electric Code, NFPA 70, requires GFCIs to be installed in more locations than previously required. For example, GFCIs are now required in some situations within residences, closer to sinks, at washing machines, and outdoors. Some of these locations may be known to promote increased leakage of current to ground, such as outdoor locations and locations near water sources. The proliferation of GFCIs in more extreme environments may lead to increased tripping of GFCIs.
At the same time, certain appliances are designed to allow an increased amount of leakage of current to ground. For example, computers are known to allow a relatively large amount of leakage to ground. Such “leaky” appliances and electronic devices may also lead to increased tripping of GFCIs.
Often, a GFCI trip is a nuisance, in that it does not represent a true fault to ground. For example, a GFCI may have a tripping threshold of 5 mA. A computer may allow 3 mA of leakage. Two computers being supplied power through a GFCI may, then, allow 6 mA of leakage, thereby tripping the GFCI, even there is no “true” ground-fault. Such tripping of GFCI devices may be considered a nuisance.
When a GFCI device is repeatedly tripping, it may be difficult to determine the cause of the tripping. For example, the GFCI may, itself, be faulty. Alternatively, the GFCI may be operating properly, but the ambient leakage may be relatively high. Alternatively, noise-causing devices may cause tripping. As yet another possibility, leaky appliances or electronic devices may cause tripping. (See below.)
Determining whether the GFCI is defective and self-tripping or if the appliance connected to the GFCI is causing it to trip may be time consuming and difficult. Determining which appliance, leakage source, and/or noise source is causing tripping may be particularly difficult because of the intermittent nature of certain nuisance tripping. Simply plugging an appliance into another GFCI or plugging a different appliance into the same GFCI may not give a result or may give a misleading result because a nuisance trip phenomena may frequently be a combination of electrical noise plus leakage to ground due moisture or humidity. Such tripping factors (e.g. noise, leakage) may vary over time, further complicating the task of identifying tripping conditions.
Thus, there is a need for methods and systems that can efficiently diagnose tripping conditions on power lines and/or ground that cause tripping of a GFCI device. There is also a need for methods and systems that can identify conditions on a power line that may cause tripping. There is another need for methods and systems that can enhance the usability of GFCI devices by identifying circumstances under which they can properly trip, and circumstances under which tripping may be a nuisance. Additionally, there is a need for a cost-effective instrument that can efficiently diagnose tripping conditions to determine whether tripping of a GFCI device is a nuisance (e.g. noise and/or ambient leakage), a defect in the GFCI device itself, or a defective appliance. The presently described technology can meet at least one of these needs.